In a reactive composition, (meth)acrylic acid esters are one important component of monomers for copolymerization and are blended for a variety of diversified purposes/applications. However, polyfunctional monomers generally added as a crosslinking component intrinsically exhibit crystallinity at room temperature or a temperature lower than that or are a compound having very high viscosity. Therefore, the viscosity of the reactive composition as a whole is often increased and handling becomes difficult.
For example, in a coating application such as hard coating or in an ink composition for inkjet printing, a (meth)acrylate of a polyfunctional alcohol represented by a pentaerythritol such as tripentaerythritol, dipentaerythritol, ditrimethylolpropane and diglycerin, and a polymerization product of trimethylolpropane, glycerin, etc. must be blended so as to impart mechanical strength or chemical stability to the reactive composition after curing. However, since the polyfunctional (meth)acrylate such as, dipentaerythritol (meth)acrylate used in the above-described reactive composition for general purposes has very high viscosity in itself and causes a great increase in the viscosity of the reactive composition, dilution with an organic solvent is required, which is not preferable also in view of VOC regulations. Furthermore, in the application such as film coating, the polyfunctional (meth)acrylate raises a problem that the film coated is curled (warped) due to cure shrinkage.
In other applications such as a resin composition for dry film resist, color resist or black resist, in addition to the requirement for film physical properties after curing, it is required to complete the curing even with a low exposure amount, that is, exhibit high sensitivity, at the time of curing with an active energy ray such as ultraviolet ray and electron beam. Above all, in a highly light-shielding composition wherein a pigment or a dye is blended at a high concentration, such as color resist and black resist, the utility value of a material capable of curing even with a low exposure amount may be extremely high.
As described above, the conventionally used (meth)acrylate of a polyfunctional alcohol has mechanical properties expected for the polyfunctional structure as well as undesired properties such as high viscosity, high crystallinity and high cure shrinkage.
As means to improve this problem, an alkylene oxide-modified polyfunctional alcohol, for example, an ethylene oxide-modified acrylate of dipentaerythritol, has been recently launched on the market. Although a compound where a long-chain alkylene oxide having an addition mol number exceeding 5 mol/hydroxyl group is introduced can achieve reduction in the viscosity or crystallinity, the original mechanical strength expected for the polyfunctional structure cannot be maintained due to decrease in the crosslinking density. However, it is known that the above-described defect of the conventional alkylene oxide-unmodified polyfunctional (meth)acrylate cannot be improved only by merely decreasing the addition mol number.
The inventors of the present invention have found that the problem above can be solved by optimizing the alkylene oxide addition mol number of an alkylene oxide-modified dipentaerythritol (meth)acrylate and controlling the content of a poly(alkylene oxide) (meth)acrylate occurring as a by-product in the alkylene oxide addition reaction.
In this connection, although Patent Document 1 refers to the amount of an ethylene oxide derivative occurring as a by-product in an ethylene oxide-modified dipentaerythritol, only the effluent and taste are evaluated and it is preferable that the amount of the by-product is 0.5% by mass or less, which differs from the present invention in both the object and the constitution.
Also, although Patent Document 2 refers to the alkylene oxide addition mol number and physical properties for dipentaerythritol, in Examples, only a propylene oxide derivative is shown and as for the physical properties, only the viscosity is evaluated, where the viscosity is at a level which is not enough to solve the above-described problem.